Narrow Results

In YBa₂Cu_3-xNi_xO_y at about 480°C all the samples show a tetragonal phase. Comparing the structural changes at 480°C with those at room temperature, the bond lengths such as Cu(1)-O(4) and Cu(2)-O(4) vary regularly with Ni-content increasing at room temperature, but not at high temperature. It suggests that there is a close correlation between structural changes and superconductivity in this system. The difference of orthorhombic- tetragonal phase -transition is also discussed between undoped YBCO and Ni-doped YBCO at high temperature.